The research efforts described here have been designed to explore cognitive processes in man. The studies have been constructed to bridge aspects of the psychology and biology of thinking, learning, and remembering. To accomplish this, studies have explored 1) disturbances in cognition as they appear in depression, mania, schizophrenia, the hyperactivity syndrome in children, the organic dementias; 2) characteristics of changes in cognitive processes as these occur in response to potential therapeutic-psychoactive drugs in patient groups; 3) studies of drug-induced changes in cognition in normal controls; 4) measurement and manipulations of behaviors that are related to cognitive functioning in psychiatric patients as well as in normal controls.